A decrease in taurine levels in the retina of partially taurine-depleted cats is accompanied by a marked alteration of the photoreceptor structure leading to cell disfunction and subsequently to eventual blindness of cats. A specific question to be examined in this project is whether any condition resulting in a decrease of retinal taurine induces damage in the structure of the virual cells. We have observed that treatment of rats with Beta-alanine or with guanido ethansulfonate, both antagonists of taurine transport, produces a decrease of retinal taurine and thereafter an alteration of the structure of photoreceptors similar to that observed in taurine-deficient cats. The occurrence of similar effects in other species will be examined in order to confirm a general role for taurine as a stabilizer of photoreceptor membranes. The overall aim of this proposal is to investigate the mechanism of the protective effect of taurine in photoreceptors. For this purpose we shall examine different properties of retinal membranes and of isolated rod outer segments of photoreceptors obtained from control animals and from taurine-deficient animals. Specifically, we propose to investigate 1) calcium binding, uptake and retention 2) peroxidation reactions 3) anion transport-phosphate and bicarbonate 4) surface charges and membrane fluidity. We also plan to examine an eventual protective effect of taurine on experimental models of photoreceptor damage altered by known mechanisms. Specifically, photochemical damage and membrane disruption produced by oxidant agents (Fe++ and CC14) will be studied in vivo and vitro. We shall also investigate a possible role for taurine in the volume regulation of isolated rod outer segments.